The present invention relates to actuators for variable valve mechanisms of internal combustion engines.
A variable valve mechanism controls the valve lift profile (i.e., the amount and duration of lift) of one or more associated valves of an engine in response to engine operating parameters, such as, for example, engine load, speed, and driver input. Generally, the valve lift profile is set by an actuator which varies the angular position of a control shaft which, in turn, varies the angular position of the variable valve mechanism relative to a central axis of an input shaft or camshaft of the engine to which the variable valve mechanism is pivotally mounted.
Actuators for variable valve mechanisms typically include an electric motor and gearbox. One example of an actuator for a variable valve mechanism is described in commonly-assigned U.S. Pat. No. 6,019,076, which is incorporated herein by reference. The gearbox includes a worm which engages a worm gear disposed on or connected to the control shaft. When a change in the valve lift profile is desired, the electric motor rotates the worm, which, in turn, rotates the worm gear. Rotation of the worm gear pivots the control shaft relative to its central axis which, in turn, angularly positions the variable valve mechanism relative to the central axis of the camshaft to thereby establish a desired valve lift profile.
The input or camshaft of the engine is driven by the engine and rotates three-hundred sixty degrees. As stated herein, the variable valve mechanism is pivotally mounted on an input shaft or camshaft of the engine. Thus, the variable valve mechanism is subjected to torque as a result of the rotation of the camshaft or input shaft to which it is pivotally mounted. This torque is reflected from the variable valve mechanism through the control shaft and back to the actuator. A spring acts upon the worm gear and/or the control shaft to substantially balance the positive and negative peaks of the reflected torque to which the control shaft and actuator are subjected. In the static state, i.e., when the control shaft is stationary, the pressure and lead angles of the teeth of the worm and worm gear are designed such that torque reflected from the variable valve mechanism through the control shaft causes the worm and the worm gear to lock up. The locking of the worm and worm gear in the static state prevent the reflected torque from being transmitted to the motor. However, in order to pivot the control shaft, the motor must be adequately powered to unlock the worm and worm gear and to overcome the reflected torque.
During rotation of the control shaft, the worm and worm gear are no longer interlocked. Thus, the motor is subjected to the reflected torque peaks. The reflected torque peaks may reach a large enough magnitude and, if directed opposite to the direction of motor rotation, cause the worm and worm gear to lock up and the motor to stall. The motor will remain stalled until the momentary torques decrease and the motor is again able to drive the mechanism in the desired direction.
Such conventional actuators require numerous parts, complicated control means, and lash adjustment systems to compensate for tolerances in manufacturing, temperature changes, and wear. The motor and gearbox must be relatively large and powerful in order to overcome the reflected torque peaks, and thus consume a substantial amount of space. An overpowered motor is relatively expensive and heavy.
Therefore, what is needed in the art is an actuator for variable valve mechanisms that has fewer parts and is therefore less expensive.
Still further, what is needed in the art is an actuator for variable valve mechanisms that requires no lash adjustment system.
Even further, what is needed in the art is an actuator for variable valve mechanisms that is less sensitive to and less affected by reflected torque.
Moreover, what is needed in the art is an actuator for variable valve mechanisms that is less dependent upon, or which completely eliminates, the motor and gearbox, thereby reducing the overall size, weight and cost of the actuator.
The present invention provides a hydraulic actuator.
The present invention comprises, in one form thereof, an elongate cylinder having a central axis, a sidewall, a top and a bottom. The sidewall is interconnected with the top and bottom in a fluid tight manner. An elongate control shaft has a first portion disposed within the cylinder and is substantially parallel with the central axis thereof. The control shaft extends in an axial direction through the top and is engaged thereby in a fluid tight manner. A second portion of the control shaft is disposed external to the cylinder. The second portion of the control shaft is configured for being pivotally coupled to at least one variable valve mechanism. A fixed vane is disposed in sealing engagement with the sidewall, top and bottom of the cylinder, and with the first portion of the control shaft. A movable vane is in sealing engagement with the top and bottom of the cylinder. The movable vane has an inner end affixed to the first portion of the control shaft, and an outer end engaging the sidewall of the cylinder in a fluid tight manner.
An advantage of the present invention is that it has fewer parts relative to a conventional actuator, and is therefore likely to be less expensive to manufacture.
Another advantage of the present invention is that it requires no lash adjustment system.
A further advantage of the present invention is that the use of a motor and gearbox is optional, and is necessary only in applications that require relatively high speed rotation and/or high amounts of torque.
A still further advantage of the present invention is that it consumes less space and is lighter in weight than conventional actuators.